It is sometimes necessary for a mobile device to be able to autonomously determine when it is being manipulated. For example, the detection of a manipulation may allow a mobile phone to increase the brightness of its screen—previously kept at a low level for the sake of saving energy—in order to facilitate unlocking. At present, this is not carried out automatically and requires a specific operation on the part of the user (generally, a touch on the screen).
The use of an accelerometer or a magnetometer allows the movements of a mobile device to be detected, which may be attributed to a manipulation. However, these movements may also be caused by the movements of the user carrying the device and thereby lead to “false positives”. The invention aims to provide a method and an apparatus for detecting a manipulation of a mobile device (other than a simple translational movement, which occurs for example during a journey) that minimizes the risk of false positives while having a satisfactory detection rate.
The inventor has realized that false positives are essentially due to movements of the mobile device that are induced by the user's walking. These movements essentially consist of low amplitude oscillations at a frequency of the order of 1 Hz that are caused by footsteps and, occasionally, of high amplitude rotations around a vertical axis, caused by changes of course. In contrast, an intentional manipulation most frequently comprises a rotation of rather high amplitude around an axis which is generally not vertical, potentially followed by rotations of lower amplitude. The method and the apparatus of the invention take advantage of these differences in order to distinguish between intentional manipulations of the device and spurious movements resulting, in particular, from the user's walking. According to the invention, rotations only around the vertical axis are not detected as manipulations, as they are generally simple changes of course as part of the user's navigation.